Pilots and air traffic controllers are no longer allowed to use popular anti-smoking drug Chantix following findings of a study that linked the drug to mental confusion and other problems that could put passengers at risk, the Federal Aviation Administration said on Wednesday.

“It’s prudent to deem the drug no longer acceptable for use,” FAA representative Les Dorr said, as quoted by Reuters.

The drug, made by Pfizer, was approved in 2006 for sale in the U.S. and the European Union. Sales of the drug were $883 million last year and an estimated 6.5 million people have used it worldwide.

The new study made by the Institute for Safe Medication Practices, a non-profit group, and reported to the U.S. Food and Drug Administration warns against “use of Chantix among persons operating aircrafts, trains, buses and other vehicles, or in other settings where a lapse in alertness or motor control could lead to massive, serious injury.”

The study linked Chantix to a wide array of health and safety problems including accident and falls, potentially lethal heart rhythm disturbances, heart attacks, seizures, diabetes and various psychiatric disturbances.

The findings were based on an analysis of adverse events reported to the FDA saying that from May 2006 through December 2007, there were 227 reports of suicide attempts or suicide, 397 cases of possible psychosis and 525 reports of hostility or aggression.

The Institute for Safe Medication Practices posted the study online because its co-author Curt Furberg, a Wake Forest University Medical epidemiologist thought the findings too important to submit first to a medical journal, which could take six months or more to publish.

Pfizer defended the drug saying the label already contains safety warnings about driving or operating machinery. “There are few things that provide greater health benefits than quitting smoking. When considering the use of Chantix for their patients, health care providers should discuss the risks of smoking, the health benefits of quitting smoking, and the product’s efficacy and safety profile,” said a Pfizer statement, issued by a company representative, Francisco Gebauer, the New York Times reported.

Pfizer added new warnings to the drug’s label no further than February this year, when the FDA warned about the risk of mood and behavior changes. The warning also said Chantix could impair patient’s ability to drive or use heavy equipment.

Now the FDA representative Susan Cruzan said the agency was still investigating the drug’s psychiatric effects. “We agree that these findings are a signal that requires further investigation and confirmation, and the FDA has been conducting a review of the adverse events associated with Chantix.” However, an investigation into the nonpsychiatric effects of Chatix has not been initiated yet, Cruzan said.

On Friday, patients using Chantix were warned to stop taking it and to immediately call their health care providers if they experience agitation, depression, behavior changes or suicidal thoughts.

The study is intended to make the FDA to take further steps in studying the negative effects of the drug, lead researcher of the Institute for Safe Medication Practices, Thomas J Moore said. “We would not have written this report if all we had seen were the psychiatric effects, because the FDA has already issued a public health advisory on that. The nonpsychiatric elements are the ones that concern us.”